Autotransformer voltage regulator



June 17, 1958 A. s. LUFTMAN ET AL 2,839,713

AUTOTRANSFORMER VOLTAGE REGULATOR Filed Feb. 1, 1954 I l 1 ,20 l MAGNE'IRON I i s I 1 1 7 /6 T 1 I -H I 25 i s P I J 1' I I Epzz: l 5 I l 3 I MAGNETTUN /Nl/EN7'O/?S ALv/lv S. LZJFTMAN JOHN 7T GooowAv CHARLES H. b rsrzsolv TOl-ZNE V United States Patent AUTOTRANSFORMER VOLTAGE REGULATOR Alvin S. Luftman, Allston, John T. Goodway, Roslindale, and Charles H. Peterson, Redford, Mass., assignors to Raytheon Manufacturing Company, Waltham, Mass, a corporation of Delaware Application February 1, 1954, Serial No. 407,430

8 Claims. (Cl. 32343.5

This invention relates to a control circuit for a variable voltage power supply and, more particularly, relates to a system for permitting application of energy of variable voltage to an output utilization device only when said voltage is a minimum.

In certain types of equipment, particularly systems for supplying energy to a magnetron, undesirable voltage and current surges in the power supply and in the magnetron occur when full operating voltage is suddenly applied. These surges not only cause sputtering of the cathode with an attendant decrease in life of the magnetron but may cause the mugnetr to operate in an undesirable mode. In addition, these surges cause short time overloads in the power supply, thereby affecting tie life of the tubes used therein.

It is desirable, therefore, to provide means for preventing a high voltage supply from being energized above a predetermined amount unless or until the voltage varying means is set to a position corresponding to minimum voltage. Furthermore, if a power failure occurs or any element of the control circuit opens, it is essential that the voltage varying means be reset to the position corresponding to minimum voltage before full power can be reapplied.

One system for varyi the high voltage supplied to a magnetron or other ut -ization means includes a variable autotransforiner having a windin whose terminals are connected either directly to the utilization means or in parallel with a portion of the primary of a high voltage transformer which is, in turn, connected to said utilization means. The autotransforrner, which is energized by an input source of relatively low voltage, is provided with a movable Contact or arm w ch is adapted to move along the winding of the autotransformer between certain limits; which may be the ter. inch of the winding, in order to vary transformation ratio of the autotransformer. When the movable is at one of the aforesaid limits, the voltage across the output of the autotransformer, and consequently the high voltage output is a minimum while the output, voltage obtained at he other limit is a maximum.

In accordance with one embodiment of this invention, the variable autotransformer is so designed that, when set to the minii. urn position, that is, the position corresponding to minimum voltage, the movable arm closes a starting point control switch. This switch is in series with a relay coil which is energized by a suitable source whenever the switch is closed. This relay has a normally open main contact in series with the input circuit of the autotransformer. When the aforesaid switch is closed and the relay is actuated, the contact closes, thereby producing an output voltage across the terminals of the auto- 2,839,718 Patented June 17, 1958 transformer winding less than the aforementioned predetermined amount. Whenever, upon starting, the control switch is open, however, that is, whenever the autotransformer arm is not at the minimum position, when the system is started, the output voltage is zero because the input circuit is interrupted, provided that the relay is init' l ired. It is necessary, therefore, when ..siormer is set initially at other than the minimum position when the output voltage has been cut off in some manner during operation to reset the movable arm to the minimum position before a high voltage output above the predetermined amount can be obtained. Once this minimum position is obtained, a holding contact on the relay maintains the latter er rgized after the movable arm is moved away from the .iinimurn position.

Although the system just described often provides satisfactory operation, particularly at lower voltages, it sometimes happens in certain aeplications that when the relay main contact is in series with either side of the input line, considerable arcing of the Contact will occur when such contact closes because of high transient starting currents. This current surge causes pitting of the contact and the life of the relay may be reduced to a relatively few operations.

In accordance with a second embodiment of this invention, the output terminals of the autotransformer are connected across a portion of primary of a high voltage transformer and the main relay contact is positioned in the line be'vecn one of the autotransformer terminals and a tap on the high voltage transformer primary. to this arrangement, the current flowing through the relay contact becomes quite small and injury to the contact is prevented or substantially reduced. In this manner the contact used ray have low current points since the contact is never made under a heavy load condition. This arra gemcnt is particularly suitable for providing high volt-age excitation for a magnetron which tends to sputter or to oscillate in an undesired mode when suddenly subjected to a voltage in excess of some predetermined amount.

Although this arrangement permits the application of input voltage to the high volt-age output transformer, even when the relay is dron 6, this input voltage is applied across a portion or" the autotransformer winding and all of the high voltage transformer primary winding in series. Since the voltage a shed to the primary winding ofthe high voltage trau rmer is less than the line or input voltage, the outp it voltage derived from the secondary of this high voltage tr nsformer is insufficient to cause the magnetron to o la.-.

When the moving '1 has reached the minimum position and the switch has cl d, the relay is energized and its main contact is At this time the input or line voltage is a ms the entire primary winding of the high voltage transformer an the voltage across its secondary is still insullicient to permit the magnetron o cillate.

Once the autotransformer arm has been i 1 the minimum position, the holding contact or relay is closed, and the relay remair he arm can now be moved away from the min' on and the input voltage is applied across a p on only of the high voltage transformer primary and a variable portion of the autotransformer winding in series. The primary voltage and, consequentl the output voltage may now be increased as the arm is moved further away from the minimum position until the output voltage across high voltage transformer secondary is sufiiciently great to per-' mit the magnetron to oscillate. The magnitude of the output voltage is dependent upon the position of the movable arm along the autotransformer winding.

In the drawings:

Fig. l is a schematic diagram of a first embodiment of the subject invention;

Fig. 2 is a schematic diagram of a second embodiment of the subject invention; and

Fig. 3 is a view showing certain details of the autotransformer and control switch of Figs. 1 and 2.

In the drawing, like reference numerals refer to corresponding elements. In Fig. 1, an alternating current input voltage from any appropriate source, such as conventional 110 volt-60 cycle A. C. power mains, is available at input terminals to which a pair of input lines 11 and 12 are connected. One of these input lines 11 is connected through a switch 13 and a current limiting resistor 16 to one terminal 14 of the single winding 17 of a variable autotransformer 15 which includes-a movable sliding contact member or arm 18 which may be either manually or mechanically driven in electrical contact with the turns of the winding. Winding 17 may be toroidal, in which case the arm 18 is adapted to rotate about the periphery of the winding over bared portions of insulated winding turns, as shown in Fig. 3. Although a single pole switch is shown in line 11 of Fig. 1, it is possible to use a double pole switch connected in both lines 11 and 12. Furthermore, one of the two lines may be grounded. The other input line 12 is connected to the arm 18 of autotransformer 15 through the medium of a relay 20, comprising an actuating winding 22 connected across the input terminals 19, an armature 23, a normally open main contact 24 and a normally open holding contact 25.

Output terminals 14 and 28 of autotransformer winding 17 are connected to an output utilization device shown, by way of example, as a magnetron oscillator 30.

A starting point control switch 35 is connected across the holding contact 25 of relay 28 and is adapted to close whenever arm 18 reaches terminal 28 of winding 17. Control switch 35 may be mechanically linked to the control arm or may be a micro switch mounted on the autotransformer assembly 15 and actuated by the rotary element 33 of the autotransformer to which arm 18 is attached, as shown in Fig. 3.

As previously stated, whenever, for any reason, it is desired to supply high voltage to a deeenrgized output means of the magnetron type, it is essential that the latter be energized at a voltage below a certain predetermined amount. A glance at Fig. 1 will indicate that the minimum voltage will be derived across output terminals 14, 28 of the autotransformer when the arm 18 is in contact with terminal 28 of the winding since the input voltage is then applied across the entire winding and the transformation ratio of autotransformer 15 is unity. As the arm is moved away from terminal 28 and toward terminal 14, the transformation ratio is increased.

When the magnetron is initially deenergized, either because of line switch 13 being opened or because of some fault in the system, or if the arm 18 is not in the minimum position, relay coil 22 cannot be energized because control switch 35 is open and the series path, including the relay coil and the control switch, is open. Since line 12 is open, it is impossible to reapply an input voltage across a portion only of the autotransformer winding.

If the arm 18 is reset to terminal 28, however, control switch 35 is closed, relay coil 22 becomes energized and both the main contact 24 and the holding contact 25 of relay close. Since the circuit between the input or line terminal 10 and the autotransformer is now completed, a voltage is derived across the output terminals 14, 28 of the autotransformer. This voltage is equal to the input voltage, neglecting transient effects owing to winding inductance, since the transformation ratio of the autotransformer is unity. The voltage initially applied to the magnetron at the instant switch 35 closes is not sufiicient to initiate oscillations in the magnetron. Once the relay coil is energized and the relay armature actuated, the holding circuit including contact 25 shunting control switch 35, maintains the relay actuated even though arm 18 is backed off from terminal 28 and control switch 35 opened. It is then possible to adjust arm 18 until the proper voltage is obtained at the output terminals of autotransformer 15 to cause the magnetron 30 to oscillate. The holding circuit remains active until, for some reason, input power is removed from the autotransformer.

In Fig. 2, a modification of the system of Fig. 1 is shown which, in addition to the elements shown in Fig. 1, includes a high voltage transformer 40 having a pri mary winding 42 and a secondary winding 44 connected to a magnetron 30 or other output utilization device. The terminals 14, 28 of autotransformer winding 17 are connected, respectively, to one terminal 45 of the primary winding 42 of the high voltage transformer and to a tap 47 along the primary 42 by way of the main contact 24 of relay 20. The position of tap 47 will depend upon the output voltage desired; as shown in Fig. 2, the tap may be positioned at the midpoint of the primary winding. One input line 11 is connected to movable arm 18 of autotransformer 15 and the other input line 12 is connected directly to terminal 46 of primary winding 42.

If the autotransformer arm 18 is in contact with terminal 14, when switch 13 is closed, control switch 35 isclosed and the relay 20 is energized as soon as power is applied. Contact 24 thus closes immediately. In this condition, the-input voltage to the primary of the high voltage transformer is produced across its terminals 45, 46 and the voltage difference between the opposite points of the contact 24 is very small. Since the total primary voltage for the transformer 40 is then equal to the line voltage, the output voltage, that is, the voltage across the secondary 44 of transformer 40, will be insufficient to cause the magnetron to oscillate with substantial power output.

If the autotransformer arm 18 is not at point 14 when switch 13 is closed, but at some position such as 27, shown in Fig. 2, the control switch 35 will be open, relay coil 22 will not be energized, main contact 24 will be open, and the circuit between points 28 and 47 will not be closed. Now the applied input voltage will be across a portion 1427 of the autotransformer winding 17 and the primary 42 of transformer 40 in series. In this condition, the transformer primary voltage is less than the input voltage and the secondary or output voltage will still be insufficient to cause the magnetron to oscillate.

In order to apply a voltage of sufficient magnitude to enable the magnetron to commence oscillating, it is thus necessary to-return arm 18 of autotransformer 15 in contact withterminal 14 which causes the relay contact 24 in line 11 to close under conditions of minimum load in said line. Once closed, the holding circuit becomes etfective and the arm 18 may be gradually moved from the starting point 14 toward terminal 28 until the output voltage applied to the magnetron becomes sufficient to permit the latter to oscillate with the desired power output.

This invention is not limited to the particular details of construction, materials and processes described, as

. in the art.

tation commensurate with the scope of the invention within the art.

What is claimed is:

1. In combination, input terminals responsive to electrical input energy, an autotransformer including a single winding and having an adjustable sliding member connected to one of said input terminals and contacting said single winding between certain limits, an output transformer having primary and secondary windings, a portion of said primary winding being connected to the other of. said input terminals, an electromechanical device energized by said input energy and energized only in response to attainment of one only of said limits for connecting said autotransformer winding in parallel with a fixed portion of said primary winding, and output terminals connected to the ends of said secondary winding.

2. In combination, input terminals responsive to electrical input energy, an .autotransformer including a single winding and having an adjustable sliding member connected to one of said input terminals and contacting said single winding between certain limits, an output transformer having primary and secondary windings, a portion of said primary winding being connected to the other of said input terminals and another portion of said primary winding being connected to said autotransformer winding, an electromechanical device energized by said input energy and energized only in response to attainment of one only of said limits for connecting said autotransformer winding in parallel with a fixed portion of said primary winding, and output terminals connected to the ends of said secondary winding, said electromechanical device further including means responsive to energization thereof for maintaining said device energized upon subsequent movement of said member away from said one limit.

3. In combination, input terminals receptive of an input voltage, an output transformer having primary and secondary windings, an autotransformer including a single winding and having a variable sliding member connected to one of said input terminals and contacting said autotransformer winding between certain limits, a portion of said primary winding being connected to the other of said input terminals and another portion of said primary winding being connected to said autotransformer winding, an electromechanical device, means responsive only to attainment of one only of said limits by said member for initially energizing said electromechanical device, said single winding having one end connected directly to said primary winding and the other end connected to a portion of said electromechanical device during energization thereof, said input voltage being applied across the terminals of said primary winding during the attainment of said one limit, said electromechanical device further including means responsive to said energization thereof for maintaining said device encrgized upon subsequent movement of said member away from said one limit and for deriving an output voltage across the secondary winding of said output transformer whose magnitude is dependent upon the position of said sliding member.

4. In combination, input terminals receptive of an input voltage, an output transformer having primary and secondary windings, output terminal means connected to the ends of said secondary winding, an autotransformer including a single winding and a variable sliding member connected to one of said input terminals and contacting said auto-transformer winding between certain limits, a portion of said primary winding being connected to the other of said input terminals and another portion of said primary winding being connected to said autotransformer winding, an electromechanical device, means responsive only to attainment of one only of said limits by said member for initially energizing said electromechanical device, said single winding having one end connected directly to said primary winding and the other end connected to a portion of said electromechanical device during energization thereof, said input voltage being applied across the terminals of said primary winding during the attainment of said one limit, said electromechanical device further including means responsive to said energization thereof for maintaining said device energized upon subsequent movement of said member away from said one limit and for supplying an output voltage across said output terminals whose magnitude is dependent upon the position of said sliding member.

5. In combination, input terminals receptive of electrical energy, a voltage controlling device including a single winding for connection to output terminals and a variable sliding member contacting said winding between certain limits, said voltage controlling device having a portion thereof connected to one of said input terminals, a switching device including a single actuating coil and a main contactor element for insertion between the other of said input terminals and said variable sliding member, said switching device further including a control contactor in series with said actuating coil and connected mechanically to said sliding member for initially energizing said coil of said switching device and for supplying energy available at said input terminals to a portion of said single winding only when said sliding member is at one only of said limits, said switching device further including a holding contactor element in shunt with said control contactor for maintaining said switching device actuated upon subsequent movement of said sliding member away from said one limit and while said input terminals are receptive of input energy.

6. In combination, input terminals receptive of electrical energy, a voltage controlling device including a single winding having a variable sliding member connected to one of said input terminals and contacting said single winding between certain limits, an output transformer having primary and secondary windings, a portion of said primary winding being connected to the other of said input terminals and another portion of said primary winding being connected to said single winding, a switching device connected in energy-supplying relationship between said input terminals and said voltage controlling device, said switching device having a main contactor inserted in an auxiliary line between one end of said single winding and a fixed point on said output transformer, said switching device including a control switch for initially closing said main contactor only when said sliding member is at one of said limits, and means responsive to closure of said main contacts for energizing said output transformer.

7. In combination, input terminals receptive of electrical energy, a voltage controlling device including a single winding having a variable sliding member connected to one of said input terminals and contacting said winding between said limits, a portion of said primary winding being connected to the other of said input terminals and another portion of said primary winding being connected to said single winding, an output transformer, a switching device connected in energy-supplying relationship between said input terminals and said voltage controlling device, said switching device having a main contactor inserted in an auxiliary line between one end of said single winding and a fixed point on said output transformer, said switching device including a control switch for initially closing said main contactor only when said sliding member is at one of said limits, and means responsive to closure of said main contactor for energizing said output transformer, said switching device further including holding means having a contactor in shunt with said control switch for maintaining said switching device actuated upon subsequent movement of said sliding member away from said one limit and only so long as said source is supplying energy, said holding means further including means for de-actuating said switching device whenever input energy is interrupted while said sliding member is at other than said one limit.

8. In combination, input terminals receptive of electrical energy, a voltage controlling device including a single winding for connection to output terminals and having a portion thereof connected to one of said input terminals and a variable sliding member contacting said winding between certain limits, a switching device including a single actuating coil and a main contactor element for insertion between the other of said input terminals and said variable sliding member, said switching device further including a control contactor in series with said actuating coil and connected mechanically to said sliding member for initially energizing said coil of said switching device and for supplying energy available at said input terminals to a portion of said single winding'only when said sliding member is at one only of said limits.

References Cited in the file of this patent V UNITED STATES PATENTS 2,267,606 Goldstine Dec. 23, 1941 

